Metastable metal colloids and preparation

Abstract

A particulate metastable Group Ib metal colloid is prepared is formed by plating a Group Ib metal onto small nuclei in a suspension to form non-spherical particles of varying color. The preparation is stable below about 100° C., but when coated onto a support, can be used to form a visible image by application of thermal energy.

What is claimed is: 
     
       1. A particulate metastable metal colloid which, when coated on a support, can be converted from a non-spherical particulate form of a first color to a stable spherical particulate form of a second color by the application of thermal energy, said colloid comprising tabular particles consisting of nuclei less than 20 nanometers in diameter and consisting of metal compounds selected from the group consisting of noble metals, silver sulfide and nickel sulfide, said nuclei having an electrolessly plated layer of silver thereon, and being dispersed in a coatable matrix, said colloid being stable against conversion to said spherical particulate form at ambient temperature conditions. 
     
     
       2. The colloid of claim 1 wherein said noble metal is silver. 
     
     
       3. The colloid of claim 1, wherein said plated nuclei have an edge layer up to about 40 nanometers and a thickness of up to about 12 nanometers. 
     
     
       4. The colloid of claim 1, wherein said matrix comprises gelatin. 
     
     
       5. The colloid of claim 1, wherein the weight ratio of said nuclei to said matrix is from about 1:5 to 1:30, on a dry basis.